Method of producing battery plates

ABSTRACT

A method of forming battery grids or plates that includes the step of mechanically reshaping or refinishing battery grid wires to improve adhesion between the battery paste and the grid wires. The method is particularly useful in improving the paste adhesion to battery grids formed by a continuous battery grid making process (such as strip expansion, strip stamping, continuous casting) that produces grid wires and nodes with smooth surfaces and a rectangular cross-section. In a preferred version of the method, the grid wires of battery grids produced by a stamping process are deformed such that the grid wires have a cross-section other than the rectangular cross-section produced by the stamping process. The method increases the cycle life of a battery.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is a continuation of U.S. patent applicationSer. No. 09/898,660, filed Jul. 2, 2001, which is a continuation of U.S.patent application Ser. No. 09/351,418, filed Jul. 9, 1999. Thefollowing applications are incorporated herein in their entirety: U.S.patent application Ser. No. 09/898,660 and U.S. patent application Ser.No. 09/351,418.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to the modification of battery grids ofthe type used in lead-acid storage batteries, and more particularly, itrelates to a modification of the shape and/or surface finish of thebattery grids of a lead-acid storage battery to improve paste adhesionand the service life of the battery.

2. Description of the Related Art

Lead-acid storage batteries typically comprise several cell elementswhich are encased in separate compartments of a container containingsulfuric acid electrolyte. Each cell element includes at least onepositive plate, at least one negative plate, and a porous separatorpositioned between each positive and negative plate. The positive andnegative plates each comprise a lead or lead alloy grid that supports anelectro-chemically active material. The active material is a lead basedmaterial (i.e., PbO, PbO₂, Pb or PbSO₄ at different charge/dischargestages of the battery) that is pasted onto the grid. The grids providean electrical contact between the positive and negative active materialswhich serves to conduct current.

The active material of a lead-acid battery may be prepared by mixinglead oxide, sulfuric acid and water. Dry additives, such as fiber andexpander, may also be added. The active material paste is then appliedto the lead grid. The pasted plates are next typically cured for manyhours under elevated temperature and humidity to oxidize free lead (ifany) and adjust the crystal structure of the plate. After curing, theplates are assembled into batteries and electrochemically formed bypassage of current to convert the lead sulfate or basic lead sulfate(s)to lead dioxide (positive plates) or lead (negative plates). This isreferred to as the “formation” process.

The formation efficiency of lead-acid batteries depends to a greatextent on the positive plate, in particular, to the extent of conversionof lead monoxide (PbO) to lead dioxide (PbO₂) in the active positivematerial. The high electrical potential required for formation appearsto be related to the transformation of non-conductive paste materials toPbO₂. A low formation efficiency of positive plates requires a highformation charge. Inefficient charging also leads to deficiencies in theresulting batteries assembled with such plates. Typically, the initialcapacity (performance) of the battery is low if the battery is notcompletely formed, requiring additional cycling to reach specificperformance values.

The formation process has been studied for some time and it isrecognized that a number of variables affect formation efficiency. Forinstance, it is well known that by increasing the adhesion between thepaste mixture and the grid; formation efficiency can be improved. Amongother things, the increased adhesion between the grid and the pasteprovides for improved interfacial contact between the grid and pastethereby improving current flow between the grid and paste. Accordingly,certain efforts to improve battery formation efficiency have focussed onimproving the adhesion between the battery grid and paste. For example,U.S. Pat. No. 3,398,024 discloses a method for obtaining better adhesionof battery paste to a lead grid by dipping the grid in a persulfate orperborate solution prior to pasting, and then pasting the grid while itis still wet.

It is also recognized that improved adhesion between battery paste andthe grid can increase the service (cycle) life of a battery. It is wellknown that lead-acid batteries will eventually fail in service throughone or more of several failure modes. Among these failure modes isfailure due to corrosion of the grid surface. Electrochemical actioncorrodes the grid surface and reduces the adhesion between the activematerial and the grid. In most instances, failure of the battery occurswhen the grids are no longer able to provide adequate structural supportor current flow due to the separation of the active material from thegrid. Therefore, there have been efforts to improve the service life ofa lead-acid battery by increasing the adhesion of the grid material tothe active paste material.

For example, U.S. Pat. No. 3,933,524 discloses a method of increasingthe cycle life of a battery wherein antimony is deposited on a leadalloy grid in order to promote adhesion of the active materials to thegrid. It is stated that the antimony may be deposited in a number ofways including electroplating, spraying, vapor deposition, sputteringand chemical displacement.

A similar method of extending the cycle life of a lead-acid storagebattery is disclosed in U.S. Pat. No. 5,858,575. In this method, alead-calcium alloy substrate is coated with a layer of a tin,lead-antimony, lead-silver or lead-tin alloy. The layer of metal on thesurface of the grid promotes better adhesion of the active materialpaste to the grid.

Another similar method is described in U.S. Pat. No. 4,906,540 whichdiscloses a method wherein a layer of a lead-tin-antimony alloy isroll-bonded to a grid base formed of a lead-calcium alloy. It is statedthat the surface layer of the lead-tin-antimony alloy enables thebattery active material to be retained for a long period of time. Theincreased adhesion of the paste to the grid serves to improve the cyclelife of the battery.

Yet another similar method is described in Japanese Patent PublicationNo. 10-284085 which discloses a method wherein a coating of alead-antimony-selenium alloy is fused to a lead-calcium-tin alloy stripand the strip is punched and/or expanded to form battery grids. Thegrids formed by this process are believed to increase battery life.

Still another similar method is described in Japanese Patent PublicationNo. 11-054115 which discloses a method wherein a pre-coating of a denseoxide is applied to a battery grid in order to improve paste adhesion inthe battery pasting process.

Thus, it can be seen that the adhesion between a battery grid andbattery active material may affect, among other things, batteryformation processes and battery service life. Accordingly, variousmethods, such as those mentioned above, have been proposed to improvethe adhesion between a battery grid and battery active material.

While these methods may provide satisfactory solutions to the problem ofinadequate paste adhesion, they do have certain disadvantages. Forexample, each of these processes requires the incorporation of anadditional material into the grid manufacturing process. In certainprocesses, the grid must be treated with an additional chemical (e.g., apersulfate or perborate solution, or an oxide). In other processes, anadditional layer of a dissimilar metal or alloy must be deposited on thegrid by chemical (e.g., electroplating) or mechanical (e.g.,roll-bonding) means. It can be appreciated that the additional processsteps and materials required in these methods can significantly increasethe cost of manufacturing the battery grids. As a result, certainbattery manufacturers may be reluctant to incorporate these methods intoa production facility.

It is apparent that previous attempts at improving paste adhesion havefocussed on the compatibility problems between battery paste materialsand the alloys or coatings at the surface of the battery grid.Accordingly, proposed solutions to the problems of paste adhesion haveinvolved the application of a dissimilar metal or coating to the gridsurface.

However, it has been discovered that another source of the problem ofinadequate paste adhesion may be the configuration of the grid.Consequently, the effect of different battery grid making processes onpaste adhesion has been further examined.

As detailed above, grids for lead acid batteries provide structuralsupport for the active material therein, and serve as a currentcollector during discharge and a current distributor during recharge.Known arts of lead acid battery grid making include: (1) batch processessuch as book mold gravity casting; and (2) continuous processes such asstrip expansion, strip stamping, continuous casting, and continuouscasting followed by rolling. Grids made from these processes have uniquefeatures characteristic of the process and behave differently in leadacid batteries, especially with respect to the pasting process.

In the book mold casting process, molten lead is poured into a grid moldand cooled to form a grid. The surface of the grid made from book moldcasting is somewhat rough and the geometric shape of the cross-sectionof the grid wires is usually oval with a sharp angle formed at the planewhere the book mold closes. Book mold casting is a batch process and itsproductivity is much lower than other processes that are continuous innature.

In the strip expansion process, a cast or wrought lead strip is pierced,stretched above and below the strip plane, and then pulled or expandedto form a grid with a diamond pattern. The surface of the wiresperpendicular to the plane of the strip is smooth and the cross-sectionof the wires is rectangular. Stamped grids also have smooth surfaces anda rectangular cross-section in the wires. For continuous casting, thesurface of the grid can be rough on the mold side and is smooth on thebelt/air side. The geometry of the cross-section of the wires producedby continuous casting can be a triangle, a trapezoid, a section of anarc or a semi-circle, depending on the mold design. If the grids arerolled after casting, the surfaces become smooth and the cross-sectionof the grid wires become rectangular.

When applying battery paste to a grid, an oval-shaped wire, such as thatin a book mold cast grid, allows the paste to flow around the wire. Therough surface and the sharp angle of the wires provide a mechanicalgraft and interlock of paste particles. Therefore, the contact betweenthe grid and the battery paste is good and the plate is strong. Withrectangular wires, on the other hand, it is much more difficult to makegood contact between the battery paste and the surface of the wiremoving in a direction perpendicular to the direction in which the pasteis applied because the flow of paste must change in a 90 degree step.This is analogous to the situation where water flows down a 90 degreecliff, and the surface right below the edge of the cliff is notcontacted by the falling water. With a grid wire orientation other than90 degrees, the change of paste flow is gradual and continuous andtherefore, provides better paste coverage. When the battery paste iscured and dried, it will shrink and generate tensile force at thepaste/grid interface. The tensile force at the paste/grid wire interfaceis at a maximum when the wire surface is perpendicular to the gridsurface and at a minimum when the wire surface is parallel to the gridsurface. As a result, a gap is formed between the grid wire and thepaste at the location where the tensile force is the maximum. This typeof plate is weak and the paste will fall off easily. Because of a lackof contact between the paste and the grid, a battery made with this typeof plate is much more difficult to form, performs poorly in certainreserve capacity tests, and does not exhibit satisfactory cycle life.

Therefore, there continues to be a need in the battery manufacturingfield for alternative methods for improving the adhesion of batterypaste active material to the battery grid. More particularly, there is aneed for a method that can increase the adherence of battery activematerial to a battery grid produced by a continuous process, such asstrip expansion, strip stamping, or continuous casting, without the needfor additional materials such as treatment chemicals or metal coatings.

It is therefore an object of the present invention to provide a methodthat increases the cycle life of a battery by enhancing the adhesionbetween the battery active material and the battery grid.

It is a further object to provide a method that increases the formationefficiency of a battery by enhancing the adhesion between the batterypaste material and the battery grid.

It is yet another object to provide a method that can modify the wiresof a battery grid made from a continuous process to mimic the wire shapeobserved in a book mold gravity cast battery grid so that the paste canflow around the grid wires to improve the plate strength.

It is yet another object of the present invention to provide a method ofmaking battery grids that allows a battery manufacturer to takeadvantage of a low cost continuous grid making process without thedrawbacks associated with inadequate paste adhesion such as reducedformation efficiency and reduced cycle life.

SUMMARY OF THE INVENTION

The foregoing needs in the art and the foregoing objects are achieved bya method of forming battery grids or battery plates that includes thestep of mechanically reshaping or refinishing battery grid wires toimprove contact between the battery paste and the grid wires. As aresult of this reshaping or refinishing of the grid wires, pasteadhesion is increased thereby increasing battery formation efficiencyand battery cycle life.

In one version of the invention, a battery grid is formed by a methodthat includes the steps of forming a preform battery grid and thenreshaping or refinishing the grid wires of the preform battery grid toform a finished grid. The preform battery grid includes a grid networkbordered by a frame element on at least one side. The top frame elementhas a current collector lug. The grid network comprises a plurality ofspaced apart grid wire elements with opposed ends. Each of the opposedends of each grid wire is joined to one of a plurality of nodes todefine open spaces in the grid network. In the reshaping or refinishingstep, at least a portion of the grid wire elements of the preformbattery grid are deformed at a position between the opposed ends of thegrid wire element. After deformation, a first transverse cross-sectiontaken at a position intermediate between the opposed ends of the gridwire element differs from a second transverse cross-section taken at oneof the opposed ends of the grid wire element. This version of theinvention is particularly useful in improving the paste adhesion toindividual battery grids formed by a continuous process (such as stripexpansion, strip stamping, continuous casting) that produces grid wiresand nodes with smooth surfaces and a rectangular cross-section. Forexample, individual grids formed by stamping process will typically havegrid wires and nodes with smooth surfaces and a generally rectangularcross-section. In this version of the invention, the grid wires of thebattery grids produced by the stamping process are deformed such thatthe grid wires have a cross-section other than the rectangularcross-section produced by the stamping process. The nodes and theopposed ends of each grid wire that are attached to each node retain agenerally rectangular cross-section so that the grid surface retains aplanar configuration.

While the method of the invention is advantageous when applied toindividual battery grids, it is particularly advantageous when employedas part of a continuous battery plate making process. For instance,another version of the invention includes the steps of forming a stripof interconnected battery grids from a grid material, reshaping orrefinishing the grid wires of each of the interconnected battery grids,applying battery paste to the strip, and cutting the strip to form aplurality of battery plates. In this version of the invention, each ofthe interconnected battery grids includes a grid network bordered by aframe element on at least one side. The top frame element has a currentcollector lug. The grid network comprises a plurality of spaced apartgrid wire elements with opposed ends. Each of the opposed ends of eachgrid wire is joined to one of a plurality of nodes to define open spacesin the grid network. In the reshaping or refinishing step, at least aportion of the grid wire elements of the interconnected battery gridsare deformed at a position between the opposed ends of the grid wireelement. In this version of the invention, the strip of interconnectedbattery grids may be formed from a grid material by any of a number ofmethods including: (1) a stamping process wherein a continuous strip ofgrid material is fed along a path and grid material is punched out ofthe strip to form the strip of interconnected battery grids; (2) acontinuous casting process wherein a grid material is melted andcontinuously cast to form the strip of interconnected battery grids; or(3) a strip expansion process wherein a continuous strip of gridmaterial is fed along a linear path, apertures are pierced in the stripof grid material, and the strip is laterally expanded to form the stripof interconnected battery grids. In this version of the invention, thegrid wires may be reshaped or refinished in a variety of manners. In onevariation of this version of the invention, the grid wires are deformedby a stamping die at a position between the opposed ends of the gridwire element.

The present invention also relates to a battery grid formed using themethod of the present invention. The improved battery grid has a gridnetwork bordered by a frame element on at least one side. The top frameelement has a current collector lug. The grid network comprises aplurality of spaced apart grid wire elements, wherein each grid wireelement has opposed ends and each of the opposed ends is joined to oneof a plurality of nodes to define a plurality of open spaces. At least aportion of the grid wire elements have a first transverse cross-sectiontaken at a position between the opposed ends of the grid wire elementthat differs from a second transverse cross-section taken at one of theopposed ends of the grid wire element. In other words, the intermediateportion of the grid wire has a shape different from the shape of theopposed ends of the grid wire where the grid wire and node meet. Thecross-section of the intermediate portion of the grid wire may be anynumber of shapes including diamond, rhomboid, hexagon, octagon or oval.Alternatively, the intermediate portion of the grid wire elements mayhave a cross-section that is rotated about 20 to about 70 degrees inrelation to the cross-section of the opposed ends of the grid wire wherethe grid wire and node meet. In this version of the invention, it ispreferred that a major portion of the intermediate portion of the gridwire elements be rotated about 20 to about 70 degrees.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other features, aspects, objects, and advantages of thepresent invention will become better understood upon consideration ofthe following detailed description, appended claims and accompanyingdrawings where:

FIG. 1 shows a front view of a battery grid made in accordance with oneversion of the method of the present invention;

FIG. 2 shows a cross-section of a vertical grid wire section taken alongline 2-2 of FIG. 1;

FIG. 3 shows a cross-section of a vertical grid wire section taken alongline 3-3 of FIG. 1;

FIG. 4 shows a cross-section of a vertical grid wire section taken alongline 4-4 of FIG. 1;

FIG. 5 shows a cross-section of a vertical grid wire section taken alongline 5-5 of FIG. 1;

FIG. 6 shows a cross-section of a vertical grid wire section taken alongline 6-6 of FIG. 1;

FIG. 7 is a photomicrograph of a transverse cross-section of a batteryplate prepared using a conventional stamped battery grid;

FIG. 8 is a photomicrograph of a transverse cross-section of a batteryplate prepared using one version of a battery grid made in accordancewith the present invention;

FIG. 9 is a photomicrograph of a transverse cross-section of a batteryplate prepared using another version of a battery grid made inaccordance with the present invention;

FIG. 10 is a photomicrograph of a transverse cross-section of a batteryplate prepared using yet another version of a battery grid made inaccordance with the present invention;

FIG. 11 is a photomicrograph that shows a front view of a battery gridmade in accordance with the method of the present invention;

FIG. 12 is a photomicrograph that shows another front view of a batterygrid made in accordance with the method of the present invention;

FIG. 13 is a photomicrograph that shows another front view of a batterygrid made in accordance with the method of the present invention; and

FIG. 14 is a photomicrograph that shows another front view of a batterygrid made in accordance with the method of the present invention.

It should be understood that the drawings are not necessarily to scaleand that the embodiments are sometimes illustrated by graphic symbols,phantom lines, diagrammatic representations and fragmentary views. Incertain instances, details which are not necessary for an understandingof the present invention or which render other details difficult toperceive may have been omitted. It should be understood, of course, thatthe invention is not necessarily limited to the particular embodimentsillustrated herein.

Like reference numerals will be used to refer to like or similar partsfrom Figure to Figure in the following description of the drawings.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 shows a front view of a battery grid made in accordance with oneversion of the method of the present invention. The grid is a stampedgrid made of a lead alloy, and functions in the same manner as otherbattery grids known in the art. It should be noted that an infinitenumber of grid designs may result from the present invention andtherefore, it is not the intent of the following description to limitthe invention to the grid design shown in FIG. 1, which is presented forthe purposes of illustration.

Referring now to FIG. 1, the grid 10 comprises a frame that includes atop frame element 12, first and second side frame elements 14 and 16,and a bottom frame element 18. The grid 10 includes a series of gridwires that define open areas 20 that hold the electrochemical paste (notshown) that provides the current generation. A current collection lug 22is integral with the top frame element 12 and is offset from the centerof the top frame element 12. The top frame element 12 includes anenlarged conductive section 24 directly beneath the lug 22, and has theshape shown to optimize current conduction to the lug 22.

A series of radially extending vertical grid wire elements 26(a)-26(o)form part of the grid 10. The vertical wire elements 26(c)-26(n) areconnected to the top frame element 12 and the bottom frame element 18,the vertical wire elements 26(a)-26(b) are connected to the top frameelement 12 in the first side frame element 14, and the vertical wireelement 26(o) is connected to the top frame element 12 and the sideframe element 16, as shown. The vertical wire element 26(i) is parallelto the side elements 14 and 16, and the remaining vertical wire elements26(a)-26(h) and 26(j)-26(o) extend radially toward an imaginaryintersecting point along a radius line running through the verticalelement 26(i). The vertical wire elements 26(a)-26(o) become closertogether when moving from the bottom element 18 towards the top element12 and get farther apart when moving towards the left element 14 or theright element 16 from the vertical element 26(i).

The grid 10 also includes a plurality of horizontal or cross wireelements. The cross wire elements include a set of parallel horizontalwire elements 30 positioned in a middle portion of the grid 10.Additionally, the grid 10 includes a first set of cross wire elements 32connected between the left frame element 14 and the vertical element26(a) that are parallel to each other, a second set of cross wireelements 34 connected between the vertical elements 26(a) and 26(b) thatare parallel to each other, and a third set of cross wire elementsconnected between the vertical elements 26(b) and 26(c) that areparallel to each other at the left side of the grid 10. Also, the grid10 includes a fourth set of cross wire elements 38 connected between thevertical elements 26(n) and 26(o) that are parallel to each other and afifth set of cross wire elements 40 connected between the verticalelement 26(o) and the right frame element 16 that are parallel to eachother at the right side of the grid, as shown. A series of short supportwires 42 are connected to the bottom frame member 18 as shown.

Individual sections of the vertical wire elements 26(a)-26(o) and thehorizontal wire elements 30 or the cross wire elements 32-40 haveopposed ends 43 which are joined at a plurality of nodes 44 that definethe open areas 20 that support the electrochemical paste for conduction.

The grid wire cross-sections shown in FIGS. 2-5 illustrate variousversions of a grid wire section formed by the method of the inventiondescribed below. In the battery grid, each grid wire section may have adifferent cross-sectional configuration, or each grid wire section mayhave the same cross-sectional configuration. However, it is preferredthat each grid wire section have the same cross-sectional configuration.It is also important to note that although certain features of theinvention have been illustrated in FIGS. 2-5 by way of cross-sectionalviews of vertical grid wires, the same cross-sectional views could applywhen taking a cross-section of horizontal grid wires. In other words,the similar deformation methods as illustrated in FIGS. 2 to 5 can alsobe applied to the horizontal wire elements. Depending on the needs, agrid can be deformed at the vertical wire elements only, or at both thevertical and horizontal wire elements.

FIG. 2 shows a cross-section of a section of vertical wire element 26(h)taken at a position between the opposed ends of the grid wire section.It can be seen that at the position between the opposed ends of thisgrid wire section, the cross-section of the grid wire is substantiallyan octagon, while the cross section of the node and the end of the gridwire section (which are shown in phantom) are substantially rectangular.It can be appreciated by those in the art that a battery grid wiresection or node will not have a perfect geometric configuration and thatthe rounding of edges and corners of a grid wire section or node isoften the result of a manufacturing operation. For this reason, thedescription of cross-sectional shapes in the specification will beproceeded by the word “substantially” to indicate that thecross-sectional shape may vary somewhat from a perfect geometric shape.

FIG. 3 shows a cross-section of a section of vertical wire element 26(i)taken at a position between the opposed ends of the grid wire section.It can be seen that at the position between the opposed ends of thisgrid wire section, the cross-section of the grid wire has been rotated45 degrees in relation to the node and the end of the grid wire section(shown in phantom), which have a substantially rectangularcross-section.

FIG. 4 shows a cross-section of a section of vertical wire element 26(j)taken at a position between the opposed ends of the grid wire section.It can be seen that at the position between the opposed ends of thisgrid wire section, the cross-section of the grid wire is substantially ahexagon, while the cross section of the node and the end of the gridwire section (which are shown in phantom) are substantially rectangular.

FIG. 5 shows a cross-section of a section of vertical wire element 26(k)taken at a position between the opposed ends of the grid wire section.It can be seen that at the position between the opposed ends of thisgrid wire section, the cross-section of the grid wire is substantially adiamond, while the cross section of the node and the end of the gridwire section (shown in phantom) are substantially rectangular.

FIG. 6 shows a cross-section of a section of vertical wire element 26(l)taken at a position between the opposed ends of the grid wire section.This figure shows the configuration of a conventional stamped batterygrid wherein the cross section of the node and the cross-section at allpositions along the grid wire section are substantially rectangular andthe surfaces of the node and grid wire section are smooth.

Upon review of FIGS. 2-5, it can be seen that in the embodiments shownin FIGS. 2, 4 and 5, the deformed cross-sectional area of each grid wiredoes not extend above or below opposed flat planar surfaces 33 of thegrid. In FIG. 3, the rotated cross-section of the grid wire does extendabove and below the planar surfaces 33 of the grid because of the natureof the forming process used to deform the grid wire. The opposed planarsurfaces 33 of the grid are formed by the grid network and the frames,and may vary slightly from a geometric flat planar surface due tomanufacturing variability.

The grid shown in FIGS. 1-5 may be manufactured by any of a number ofversions of the method of the present invention. In a preferred versionof the invention, the battery grid is produced as part of an automatedbattery plate making process that includes grid stamping operations. Inthis version of the invention, a conventional lead or lead alloy batterygrid material (such as a lead-calcium-tin alloy) is melted andcontinuously cast to form a continuous strip of grid material. Thecontinuous strip may then be rolled to modify the thickness or grainstructure of the strip. A series of interconnected battery grids is thenformed by punching grid material out of the continuous strip.

During the punching operations, the strip is maintained as a continuousstrip and preferably the interconnected grid shapes are formed in aprogressive punching operation, i.e. features are added to the batterygrid through several punching operations. Preferably, each of theinterconnected battery grids has a grid network bordered by a frame asshown in FIG. 1 and described above. However, it is also possible toform interconnected battery grids having a grid network bordered by oneor more separate frame elements.

After the punching operations form a strip having interconnected grids,the battery grid wire sections of the strip are processed in a stampingstation. The stamping station is used to deform or coin the grid wiresso that the grid wires have a cross-section similar to one of the gridwire cross-sections shown in FIGS. 2-5. For instance, the stampingstation may include a die that deforms the rectangular cross-section ofthe grid wires of the punched grid into an octagonal cross-section asshown in FIG. 2. Alternatively, a stamping die may be used that rotatesthe intermediate portion of the grid wire elements about 20 to about 70degrees in relation to the cross-section of the opposed ends of the gridwire where the grid wire and node meet as depicted in FIG. 3.

It can be appreciated that any number of modified grid wire shapes canbe selected as long as the shape provides paste adhesion characteristicsthat are superior to the rectangular cross-section produced by astamping process. Preferably, the modified grid wire substantially has adiamond shape, a rhomboid shape, a hexagon shape, an octagon shape, oran oval shape. When deforming the grid wires in the stamping station,the area of deformation along the length of the grid wire between theopposed ends of each grid wire section may vary. For example, it ispreferred that 90% of the length of the grid wire between the opposedends of the grid wire undergo deformation at the stamping station. UsingFIG. 2 as a reference, this means that 5% of the grid wire length nearone end of the grid wire section would have a rectangular cross-section,the center 90% of the grid wire length would have a substantiallyoctagonal cross-section, and 5% of the grid wire length near the otherend of the grid wire section would have a rectangular cross-section.While it is preferred that the nodes remained undeformed in this versionof the invention, in certain circumstances it may be advantageous todeform or coin the nodes in the stamping station. Since coining of thenodes as well as the grid wires will tend to make the grid stripnon-planar, pasting operations which tend to apply paste more thickly toone side of the plate than the other can benefit from this effect. Thegrid strip can then be oriented so that paste can more readily flow tothe surface which is thinly pasted, i.e., fed into the pasting machineso that the concave side faces the direction that otherwise would bethinly pasted, typically the bottom.

The interconnected grids having modified grid wires are then processedto apply battery paste and the strip is cut to form a plurality ofbattery plates. Alternatively, the interconnected grids may be cut intoa plurality of grids before pasting and stored for later use.

In other versions of the method of the invention, the interconnectedbattery grids may be formed by alternate means, such as strip expansionor continuous casting processes. In strip expansion, a continuous stripof grid material is fed along a linear path aligned with thelongitudinal direction of the strip, apertures are punched in the stripof grid material, and the strip is laterally expanded to form the stripof interconnected battery grids. In the continuous casting process, thegrid material is melted and continuously cast to form the strip ofinterconnected battery grids. Optionally, the continuous cast strip maybe rolled to achieve dimensional control or grain structuremodification. When these alternate means for forming the strip ofinterconnected battery grids are used, the strip of grids is stillfurther processed in a stamping station in order to modify therectangular cross-section of the grid wires produced in the stripexpansion or continuous casting process.

FIGS. 11-14 show a battery grid that was formed using the version of themethod of the present invention wherein the grid openings arecontinuously punched out of a lead alloy strip and the grid wires aresubjected to a coining deformation step in a stamping station. It can beseen that the areas where the opposed ends of the grid wire sectionsmeet the nodes were not subjected to deformation and therefore, theareas retain the shape formed in the continuous punching operation. Itcan also be seen that the areas of the grid openings near the nodes havea slight inner radius that results from the process.

The invention is further illustrated in the following Examples which arepresented for purposes of illustration and not of limitation.

EXAMPLE 1

A conventional stamped battery grid with grid wires having a rectangularcross-section and smooth surfaces (as depicted in FIGS. 1 and 6) waspasted with a conventional positive paste for lead acid batteries andthen cured. The cured plate was sectioned with a cutting wheel in adirection transverse to the planar surface of the plate, polished, andphotographed. The photograph is shown in FIG. 7. As FIG. 7 shows, thecured plate exhibits gaps 70 at the paste 72/grid wire 73 interfaces,and the gaps extend into the bulk paste as cracks 71.

Example 1(a)

A second conventional stamped battery grid identical to the grid used inExample 1 was substantially modified by rotating a major portion of gridwires by 45 degrees. (This version of a grid is depicted in FIGS. 1 and3.) The modified grid was then pasted with a conventional positive pastefor lead acid batteries and cured. The cured plate was sectioned with acutting wheel in a direction transverse to the planar surface of theplate, polished, and photographed. The photograph is shown in FIG. 8wherein the grid wire is designated at 80 and the paste is designated at81. It can be seen from FIG. 8 that the plate prepared using themodified grid of Example 1(a) exhibited improved paste adhesion comparedto the plate prepared using the grid of Example 1 (FIG. 7) and that theplate prepared using the modified grid of Example 1(a) exhibited areduced number of cracks.

Example 1(b)

A third conventional stamped battery grid identical to the grid used inExample 1 was substantially modified by stamping the grid wires to forma diamond-shaped cross-section. (This version of a grid is depicted inFIGS. 1 and 5.) The modified grid was then pasted with a conventionalpositive paste for lead acid batteries and cured. The cured plate wassectioned with a cutting wheel in a direction transverse to the surfaceof the plate, polished, and photographed. The photograph is shown inFIG. 9. It can be seen from FIG. 9 (wherein the grid wire is designatedat 90 and the paste is designated at 91) that the plate prepared usingthe modified grid of Example 1(b) exhibited improved paste adhesioncompared to the plate prepared using the grid of Example 1 (FIG. 7) andthat the plate prepared using the modified grid of Example 1(b)exhibited a reduced number of cracks.

Example 1(c)

A fourth conventional stamped battery grid identical to the grid used inExample 1 was substantially modified by stamping the grid wires to forman octagonal shaped cross-section. (This version of a grid is depictedin FIGS. 1 and 2.) The modified grid was then pasted with a conventionalpositive paste for lead acid batteries and cured. The cured plate wassectioned with a cutting wheel in a direction transverse to the surfaceof the plate, polished, and photographed. The photograph is shown inFIG. 10. It can be seen from FIG. 10 (wherein the grid wire isdesignated at 100 and the paste is designated at 101) that the plateprepared using the modified grid of Example 1(c) exhibited improvedpaste adhesion compared to the plate prepared using the grid of Example1 (FIG. 7) and that the plate prepared using the modified grid ofExample 1(c) exhibited a reduced number of cracks.

EXAMPLE 2

Vibration weight loss is a very good measure to evaluate the strength ofa battery plate. In order to demonstrate the effectiveness of thepresent invention, two battery plates were prepared. The first batteryplate was prepared using the procedure of Example 1, and the secondbattery plate was prepared using the procedure of Example 1(c). Thecontrol plate of Example 1 and the plate of the present invention asdescribed as Example 1(c) were then placed on a platform vibrating at afrequency of about 60 hertz with an amplitude of about three millimetersfor one minute. The plate weights before and after vibration werecompared. On average, the control plates of Example 1 lost 16 times thebattery paste that was lost in plates formed in accordance with thepresent invention of Example 1(c). This test demonstrated that whenassembled into battery plates, battery grids manufactured in accordancewith the present invention improve paste adhesion between the grid andthe paste.

EXAMPLE 3

Batteries made of conventional stamped grids and grids prepared inaccordance with the present invention as described in Example 1(c) werecycled in accordance with the SAE J240 life test procedure at atemperature of 167° F. to measure the service life. Fourteen batterieshaving grids prepared in accordance with Example 1(c) and ten controlbatteries having conventional stamped grids were tested. The averagenumber of cycles for batteries having grids prepared in accordance withExample 1(c) was 2.7 times the average number of cycles for the controlbatteries. This demonstrates that batteries including grids made inaccordance with the present invention will have better cycle lifeperformance than batteries including conventional grids.

Thus, the present invention provides a method that can increase theadherence of battery active material to a battery grid produced by acontinuous process, such as strip expansion, strip stamping, orcontinuous casting, without the need for additional materials such astreatment chemicals or metal coatings. The method of the presentinvention increases the cycle life of a battery by enhancing theadhesion between the battery paste material and the battery grid. Themethod of the invention modifies the wires of a battery grid made from acontinuous process to mimic the wire shape observed in a book moldgravity cast battery grid so that battery paste can flow around the gridwires to improve the plate strength after pasting. As a result, abattery manufacturer can take advantage of a low cost continuous gridmaking process without the drawbacks associated with inadequate pasteadhesion.

Although the present invention has been described in considerable detailwith reference to certain preferred embodiments, one skilled in the artwill appreciate that the present invention can be practiced by otherthan the preferred embodiments, which have been presented for purposesof illustration and not of limitation. Therefore, the spirit and scopeof the appended claims should not be limited to the description of thepreferred embodiments contained herein.

1. A method of producing battery plates for lead-acid batteriescomprising: providing a strip of material comprising lead; punchingmaterial out of the strip to form a plurality of interconnected grids,each interconnected grid comprising a plurality of wires having opposedends and joined to at least one of a plurality of nodes; and deformingat least one of the plurality of wires at a first position between itsopposed ends such that the deformed wire has a non-rectangularcross-sectional shape at the first position and a generally rectangularcross-sectional shape near at least one of its opposed ends.
 2. Themethod of claim 1 wherein the step of providing a strip of materialcomprises casting a strip of material and rolling the strip of material.3. The method of claim 1 wherein the step of punching material out ofthe strip comprises a progressive punching operation.
 4. The method ofclaim 1 wherein the step of deforming at least one of the plurality ofwires comprises stamping the at least one wire.
 5. The method of claim 1further comprising applying paste to the strip.
 6. The method of claim 5further comprising cutting the strip to form a plurality of batteryplates before the step of applying paste.
 7. The method of claim 6further comprising cutting the strip to form a plurality of batteryplates after the step of applying paste.
 8. The method of claim 1wherein the deformed wire has a transverse cross-sectional shape at thefirst position that is selected from the group consisting of a diamond,an oval, a rhomboid, a hexagon, and an octagon.
 9. The method of claim 1wherein the step of deforming at least one of the plurality of wirescomprises rotating the at least one wire.
 10. The method of claim 1wherein each of the interconnected grids comprises a frame havingopposed substantially planar surfaces, and wherein the at least onedeformed wire has a transverse cross-section that does not extend beyondthe planar surfaces.
 11. The method of claim 1 wherein the step ofdeforming at least one of the plurality of wires comprises deforming atleast 90 percent of the wire.
 12. The method of claim 1 wherein the stepof punching material out of the strip comprises a progressive punchingoperation.
 13. A method of producing battery plates comprising:providing a strip of material comprising lead; punching material out ofthe strip to form a plurality of interconnected grids, eachinterconnected grid comprising a plurality of wires having opposed endsand joined to at least one of a plurality of nodes; and deforming atleast one of the plurality of wires at a first position between itsopposed ends such that the deformed wire has a non-rectangularcross-sectional shape at the first position; wherein each of theplurality of interconnected grids includes a plurality of radiallyextending vertical wires and a plurality of horizontal wires and whereinthe step of deforming at least one of the plurality of wires comprisesdeforming a plurality of the vertical wires.
 14. The method of claim 13wherein the step of deforming at least one of the plurality of wirescomprises deforming a plurality of the horizontal wires.
 15. The methodof claim 13 further comprising deforming at least one of the pluralityof nodes.
 16. A method of manufacturing battery plates comprising:providing a rolled strip of material comprising lead; removing materialfrom the strip in a progressive punching operation to form a pluralityof interconnected grids, each of the plurality of interconnected gridshaving a plurality of wires, each of the wires having opposed ends thatare joined to at least one of a plurality of nodes; and deforming atleast one of the plurality of wires between its opposed ends such thatthe deformed wire has a first transverse cross-sectional shape betweenits opposed ends and a second transverse cross-sectional shape near atleast one of its opposed ends that differs from the first transversecross-sectional shape.
 17. The method of claim 16 wherein theprogressive punching operation comprises performing several punchingoperations on the strip to form the plurality of interconnected grids.18. The method of claim 16 wherein the step of deforming at least one ofthe plurality of wires comprises stamping the at least one wire.
 19. Themethod of claim 16 further comprising applying paste to the strip andcutting the strip to form a plurality of battery plates.
 20. The methodof claim 16 wherein the second transverse cross-sectional shape isgenerally rectangular.
 21. The method of claim 20 wherein the firsttransverse cross-sectional shape is selected from the group consistingof a diamond, an oval, a rhomboid, a hexagon, and an octagon.
 22. Themethod of claim 16 wherein the step of deforming at least one of theplurality of wires comprises rotating the at least one wire.
 23. Themethod of claim 16 further comprising deforming at least one of theplurality of nodes.
 24. A method of producing battery plates forlead-acid batteries comprising: rolling a strip of material comprisinglead; punching material out of the strip to form a plurality ofinterconnected grids, each interconnected grid comprising a frame havingopposed substantially planar surfaces and a plurality of wires havingopposed ends and joined to at least one of a plurality of nodes; andchanging the cross-sectional shape of at least one of the plurality ofwires at a first position between its opposed ends such that thedeformed wire has a first cross-sectional shape at the first positionand a different second cross-sectional shape near at least one of itsopposed ends, wherein no part of the deformed wire extends beyond theplanar surfaces of the frame.
 25. The method of claim 24 wherein thestep of changing the cross-sectional shape of at least one of theplurality of wires comprises stamping the at least one wire.
 26. Themethod of claim 24 further comprising applying paste to the strip andcutting the strip to form a plurality of battery plates.
 27. The methodof claim 24 wherein the second cross-sectional shape is generallyrectangular.
 28. The method of claim 24 wherein the firstcross-sectional shape is selected from the group consisting of adiamond, an oval, a rhomboid, a hexagon, and an octagon.
 29. The methodof claim 24 wherein a portion of the plurality of wires are radiallyextending vertical wires.
 30. A method of producing battery platescomprising: providing a strip of material comprising lead; punchingmaterial out of the strip to form a plurality of interconnected grids,each interconnected grid comprising a plurality of wires having opposedends and joined to at least one of a plurality of nodes; and deformingat least one of the plurality of wires at a first position between itsopposed ends such that the deformed wire has a first cross-sectionalshape at the first position selected from the group consisting of adiamond, an oval, a rhomboid, a hexagon, and an octagon, wherein thedeformed wire has a second cross-sectional shape near at least one ofits opposed ends that is different than the first cross-sectional shape.31. The method of claim 30 wherein the second cross-sectional shape nearat least one of its opposed ends is substantially rectangular.
 32. Themethod of claim 30 wherein the step of deforming at least one of theplurality of wires comprises stamping the at least one wire.
 33. Themethod of claim 30 wherein the step of deforming at least one of theplurality of wires comprises rotating the at least one wire.
 34. Themethod of claim 30 wherein each of the interconnected grids comprises aframe having opposed substantially planar surfaces, and wherein the atleast one deformed wire has a transverse cross-section that does notextend beyond the planar surfaces.
 35. The method of claim 30 whereineach of the plurality of interconnected grids includes a plurality ofradially extending vertical wires.
 36. A method of producing batteryplates comprising: providing a strip of material comprising lead;punching material out of the strip to form a plurality of interconnectedgrids having opposed substantially planar surfaces, each interconnectedgrid comprising a plurality of wires having opposed ends and joined toat least one of a plurality of nodes; and deforming at least one of theplurality of wires at a first position between its opposed ends suchthat the deformed wire has a non-rectangular transverse cross-sectionalshape at the first position, wherein the non-rectangular transversecross-section of the deformed wire does not extend beyond the planarsurfaces of the interconnected grid.
 37. The method of claim 36 whereinthe non-rectangular transverse cross-sectional shape is selected fromthe group consisting of a diamond, an oval, a rhomboid, a hexagon, andan octagon.
 38. The method of claim 36 wherein the deformed wire has atransverse cross-sectional shape near at least one of its opposed endsthat is generally rectangular.
 39. The method of claim 36 wherein thestep of deforming at least one of the plurality of wires comprises atleast one of stamping the at least one wire and rotating the at leastone wire.
 40. The method of claim 36 wherein a portion of the pluralityof wires are radially extending vertical wires.